In order to improve riding feel and comfort of an automobile, there is a need for a contrivance so that engine vibrations are not transmitted to the driver compartment. Heretofore, there has been proposed a technique for reducing automobile body vibration by imparting a vibration absorbing function to the mounting mechanism that supports an engine, or by forced excitation with use of an actuator (for example, refer to Japanese Unexamined Patent Application, First Publication No. S61-220925, and Japanese Unexamined Patent Application, First Publication No. S64-083742).
In conventional techniques, in order to control an actuator, sensors are used for detecting relative displacement, relative velocity, and relative acceleration between the actuator movable section and the fixation section. However, the sensors need to be installed in the vicinity of the engine where they are exposed to a high temperature environment, and consequently there is a problem of a lack of reliability.
Moreover, in the case of using plate springs or the like in order to ensure durability of a movable element supporting means of the actuator, a resonance system is constituted by a movable section mass and plate spring constant. However, in controlling automobile vibration, there is a problem of negative impact on vibration suppression control in that in the case where the resonance magnification is high, if the resonance frequency changes even slightly due to temperature changes or age related changes, the response of the actuator to command signals changes significantly.
Also, there is known a vibration suppression apparatus that can actively reduce vibrations of the vibration prevention target object over an entire wide frequency bandwidth by; detecting vibrations of the vibration prevention target object, passing this detection signal through a filter to thereby generate vibration waveforms that interfere with the vibrations of the vibration prevention target object and cancel out the vibrations, and applying signals based on these vibration waveforms to the actuator (for example, refer to Japanese Unexamined Patent Application, First Publication No. H03-219140).
Control is performed to automobiles of recent years that aims to improve fuel economy by stopping cylinders of a six cylinder engine as required so as to drive the engine with fewer cylinders (for example, with three cylinders). If the cylinders are stopped, there is a possibility that engine vibrations may increase compared to the vibrations in a six cylinder operation. For solving such problems, as disclosed in Japanese Unexamined Patent Application, First Publication No. H03-219140, a vibration suppression apparatus that actively reduces vibrations across a wide frequency bandwidth is effective.
However, the conventional damping apparatus performs only a control to suppress vibrations being generated. Therefore, there is a problem in that in an automobile to which control is performed to stop a predetermined number of cylinders in a six cylinder engine, all vibrations are suppressed so that it is difficult to sense that the engine is driving, and hence the driver experiences discomfort. It is desirable the driver experiences no discomfort, by suppressing the vibrations without letting the driver feel the switch from six cylinder driving to a cylinder stop operation.
There is also known a vibration control apparatus for an automobile that uses an actuator that uses reaction force occurring as a result of driving a movable section, to thereby generate a damping force according to engine revolution speed (for example, refer to Japanese Unexamined Patent Application, First Publication No. S61-220925). According to this apparatus, vibrations of the automobile body can be predicted from the revolution speed of the automobile engine, and a force applied to the automobile body from the engine can be canceled by the actuator. Therefore, it is possible to reduce vibrations of the automobile body. Such a damping apparatus uses a linear actuator that performs reciprocation, to vibrate an auxiliary mass to thereby reduce vibrations of the damping target. On the other hand, as a linear actuator, there is known a linear actuator in which an elastic supporting section (plate spring) supports a movable element at a fixed position and elastically transforms itself to thereby support the movable element (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2004-343964). In this linear actuator, no wear or sliding resistance occurs on the movable element, and even after use for a long period of time, the precision of the bearing support does not decrease, and a high level of reliability can be attained. Furthermore, there is no power consumption loss caused by sliding resistance, and an improvement in the performance can be achieved. Moreover, the elastic supporting section avoids interference with a coil and is supported on a stator in a position that is away from the coil with the movable element as a base point. Thus, it becomes possible to arrange the voluminous coil and the elastic supporting section in close proximity to each other, and therefore, a reduction in the size of the linear actuator can be realized.
Furthermore, there is known a damping apparatus which, in order to optimize damping control, prepares a plurality of data maps of amplitude and phase data according to the operating state of the automobile, and generates signals for driving the actuator that dampens vibrations based on the amplitude/phase data from the data maps which is taken out according to the operating state of the automobile (for example, refer to Japanese Unexamined Patent Application, First Publication No. H11-259147). Moreover, adaptive filters are a technique for performing damping while following the changes in the state of an automobile, and as examples of which, there are known adaptive filters realized in time domain (for example, refer to Japanese Unexamined Patent Application, First Publication No. H10-49204, and Japanese Unexamined Patent Application, First Publication No. 2001-51703) and adaptive filters realized in frequency domain (for example, refer to “Application techniques of adaptive filters”, Toshifumi Kosaka, The Journal of the Acoustical Society of Japan, volume 48, No. 7, P. 520). In any method that uses adaptive filters, control is performed such that the amplitude phase for suppressing vibrations is found by itself based on error signals (for example, acceleration signals) at a specific measuring point.
However, there is a problem in that since the operation of adaptive filter processing takes a long time, the damping effect is degraded if sudden changes occur in engine revolution speed, and in particular, the method realized in the frequency domain takes a long time for processing. There is also a problem in that if there are characteristic changes or age related changes that would cause changes in the transfer function from the command values for the actuator to the signals at the measuring point (acceleration), the damping characteristic is degraded. On the other hand, with the method that makes reference to the map data to perform control, processing time can be reduced and it is therefore possible to improve response. However, there is a problem in that individual differences or age related changes of the actuator used for the control or the damping target engine cause degradation in the damping performance.
Furthermore, in the case where an auxiliary mass (weight) is attached to the linear actuator, and the reaction force that occurs when vibrating this auxiliary mass is used to perform damping control for suppressing vibrations of the target device, an amplitude command value and frequency command value are found based on the vibration state value of the control target device, and the value of current to be applied to the linear actuator is controlled according to this amplitude command value and frequency command value. By attaching such a damping apparatus to the body of an automobile, the force from the engine of the automobile being applied to the automobile body can be cancelled out, and therefore it is possible to reduce vibrations of the automobile body.
However, there is a problem in that if there is occurring an external force (disturbance) that is close to the natural frequency determined from the auxiliary mass fixed on the movable element and the plate spring that holds this movable element, or if a driving command value that is close to the natural frequency is inputted, then excessive amplitude occurs due to resonance, and a force greater than the required reaction force for damping occurs, making the linear actuator unable to perform appropriate vibration suppression control.
Moreover, there is a problem in that since there is structurally provided a stopper of the movable element in order to limit the movable range of the movable element, in the case where changes in the behavior of the automobile become significant as a result of the automobile suddenly accelerating or traveling over a rough road surface, an external force acts on the auxiliary mass. Consequently, excessive amplitude occurs so that there is a problem in that a phenomena where the movable element collides with the stopper occurs. Furthermore there is a problem in that, in the case where changes in the behavior of the automobile are significant, changes in current for driving the linear actuator also becomes more significant proportionately, and the movable element consequently collides with the stopper. If the movable element collides with the stopper, the sound of collision occurs as an abnormal noise. Also there is a problem in that if too many collisions occur between the movable element and the stopper, there will be a greater chance of reduced lifetime of the components that constitute the linear actuator.